python：用两个嵌套循环迭代数组

Question

The goal of this loop is, for each star element (composed of x and y coords in the form of [int, int] ) in the list stars , calculate the distance and angle to every other star

#list to store lists of distances
star_map = []

#go through each star to calculate distance from this star
for star in stars:

    print("main loop")

    sub_map = [] #list of distances from this star


    for sub_star in stars: 

        print("sub loop")

        #find distance
        dx = float(star[0]-sub_star[0])
        dy = float(star[1]-sub_star[1])

        #if distance is zero, break because it's the same star
        if(dx == 0 and dy == 0):
            break

        #otherwise get distance and angle    
        dist = np.sqrt(dx ** 2 + dy ** 2)
        theta = get_theta(dx, dy)

        #add it to a list of distances from this star
        sub_map.append((dist, theta))
        print("sub loop")

    #add the list of distances from this star to the main list    
    star_map.append(sub_map)

What I would expect is that it prints one "main loop" followed by "sub loop" len(stars) - 1 times. (-1 because once, the star in the inner and outer loops is the same, and I want to ignore that)

What happens is that I get this:

main loop
main loop
sub loop
main loop
sub loop
sub loop
main loop
sub loop
sub loop
sub loop

etc, etc, until the last loop, when it prints the expected number of "sub loop" lines.

ie each time, it loops through one more star.

Why is this happening, and how can I loop through every star, every time?

Edit: The problem was that instead of using continue, I used break to stop the loop when the star in the sub loop was the same as the outer loop. Changing to continue fixed this.

Answer 1

The break statement will cause the sub loop to break and revert back to the main loop when it encounters the same star. What you want is for the sub loop to skip this iteration. Try using continue instead of break .